Back pack



FIG. 1 is a front, top, right side perspective view of a back pack showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a back elevational view thereof; and,

FIG. 6 is a bottom plan view thereof.

The dot-dash-dot broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design.

The dash-dash-dash broken lines shown in the drawings represent stitching lines. 

We claim the ornamental design for a back pack, as shown and described. 